Serious spinal cord injuries (SCI) affect approximately 1.3 million people in the United States, and roughly 12-15,000 new injuries occur each year. Of these injuries, approximately 50% are complete spinal cord injuries in which there is essentially total loss of sensory motor function below the level of the spinal lesion.
Neuronal networks formed by the interneurons of the spinal cord that are located in the cervical and lumbar enlargements, such as the spinal networks (SNs), play an important role in the control of posture, locomotion and movements of the upper limbs, breathing, swallowing and speech. Most researchers believe that all mammals, including humans, have SNs in the lunbosacral cord. See Dimitrijevic, M. R, Gerasimenko, Yu., and Pinter, M. M., Evidence for a Spinal Central Pattern Generator in Humans, Ann. N. Y. Acad. Sci., 1998, vol. 860, p. 360; Gurfinkel', V. S., Levik, Yu. S., Kazennikov, O. V., and Selionov, V. A., Does the Prime Mover of Stepping Movements Exist in Humans?, Human Physiology, 1998, vol. 24, no. 3, p. 42; Gerasimenko, Yu. P., Roy, R. R., and Edgerton, V R., Epidural Stimulation: Comparison of the Spinal Circuits That Generate and Control Locomotion in Rats, Cats and Humans, Exp. Neurol., 2008, vol. 209, p. 417. Normally, the activity of SNs is regulated supraspinally and by peripheral sensory input. In the case of disorders of the connections between the brain and spinal cord, e.g., as a result of traumatic spinal cord lesions, motor tasks can be enabled by epidural electrical stimulation of the lumbosacral and cervicalsegments as well as the brainstem. It has been shown that epidural electrical spinal cord stimulation (eESCS) with enough intensity can induce electromyographic (EMG) patterns in the leg muscles of patients with clinically complete spinal cord injury. See Dimitrijevic, Gerasimenko, Yu., and Pinter, supra; Minassian, K., Persy, I., Rattay, F, Pinter, M. M., Kern, H., and Dimitrijevic, M. R., Human Lumbar Cord Circuitries Can Be Activated by Extrinsic Tonic Input to Generate Locomotor-Like Activity, Human 1Hovement Sci., 2007, vol. 26, p. 275. But the novelty of the approach described in this document is that the spinal circuitry can be neuromodulated to a physiological state that facilitates or enables the recovery or improved control of movement without actually inducing the movement following some neuromotor dysfunction. Harkema, S., Gerasimenko, Y, Hodes, J., Burdick, J., Angeli, e., Chen, Y, Ferreira, e., Willhite, A., Rejc, E., Grossman, R. G., and Edgerton, V R., Epidural Stimulation of the Lumbosacral Spinal Cord Enables Voluntary Movement, Standing, and Assisted Stepping in a Paraplegic Human, Lancet, 2011, vol. 377, p. 1938. eESCS is an invasive method and requires surgical implantation of electrodes on the dorsal surface of the spinal cord, which limits this method of activating SNs to clinics.
Recently, noninvasive methods for activating the SNs by means of leg muscle vibration and spinal cord electromagnetic stimulation was suggested. It was found that the vibration of the tendons of the hip muscles initiates involuntary walking movements in subjects lying on their side with an external support for the legs. See Gurfinkel', V S., Levik, Yu. S., Kazennikov, O. V, and Selionov, V A., Locomotor-Like Movements Evoked by Leg Muscle Vibration in Humans, Eur. J lVeurosci., 1998, vol. 10, p. 1608; Selionov, V A., Ivanenko, Yu. P., Solopova, l A., and Gurfinkel', VS., Tonic Central and Sensory Stimuli Facilitate Involuntary Air-Stepping in Humans, J Neurophysiol., 2009, vol. 101, p. 2847. In addition, electromagnetic stimulation of the rostral segments of the lumbar spinal cord caused involuntary walking movements in healthy subjects in a similar position with a support for the legs. See Gerasimenko, Yu., Gorodnichev, R., Machueva, E., Pivovarova, E., Semenov, D., Savochin, A., Roy, R. R., and Edgerton, V R., Novel and Direct Access to the Human Locomotor Spinal Circuitry, J New'osci., 2010, vol. 30, p. 3700; Gorodnichev, R. M., Machueva, E. M., Pivovarova, E. A., Semenov, D. V, Ivanov, S. M., Savokhin, A. A., Edgerton, V R., and Gerasimenko, Yu. P., A New Method for the Activation of the Locomotor Circuitry in Humans, Hum. Physiol., 2010, vol. 36, no. 6, p. 700. Step-like movements elicited by vibration and electromagnetic stimulation, have apparently a different origin. In the former case, the SN is activated by afferent input mainly due to the activation of muscle receptors, whereas in the latter case, the neuronal locomotor network is affected directly. Each of these methods has its specificity. For example, the vibratory muscle stimulation elicits involuntary locomotor movements only in the hip and knee joints, without the involvement of the ankle. In addition, these characteristic movements could be evoked only in 50% of the subjects. See Selionov, Ivanenko, Solopova, and Gurfinkel', supra. The percentage of subjects in whom the spinal cord electromagnetic stimulation evoked involuntary step like movements was even smaller (10%), although in this case, the kinematic structure of the resultant movements was consistent with the natural random step-like movements to a greater extent than in the case of vibration. See Gerasimenko, Gorodnichev, Machueva, Pivovarova, Semenov, Savochin, Roy, and Edgerton, supra; Gorodnichev, Machueva, Pivovarova, Semenov, Ivanov, Savokhin, Edgerton, and Gerasimenko, supra. In addition, spinal cord electromagnetic stimulation is limited by the technical capabilities of the stimulator. The modem magnetic stimulator used in clinics (e.g., Magstim Rapid) can provide only short-exposure stimulating effects. The electromagnetic stimulator, with the parameters required to elicit step-like movements (5 Hz and 1.5 T), could be sustained for only 15 s.
Accordingly, a need exists for the further development of neuromodulation systems and devices.